The present invention generally relates to a translucent adhesive film composition.
The market for polymer films is enormous and is continually growing with a major component of that market being for packaging. Exceptional difficulties have been encountered in applying conventional adhesives to polymeric films, and in particular ionic films. Ionic films may be characterized as hydrophobic films having a polyethylene backbone to which carboxylic acid groups are attached. The carboxylic acid groups may be partially or completely neutralized with metal ions. During application of an adhesive to the ionic film, incomplete coverage of the ionic film by the adhesive typically occurs since the metal ions on the surface of the ionic film may prevent wetting by the adhesive. Incomplete coverage of the ionic film by the adhesive may impair adhesion of the ionic film to a surface, for example. In addition, incomplete coverage may promote undesirable delamination of the ionic film from the bonding surface after a certain period of time has elapsed.
Furthermore, use of special techniques and/or equipment may be required during application of the adhesive to the ionic film. As an example, the adhesive may require heating to very high temperatures or application using high pressures in order to obtain a substantially adhesive bond between the ionic film and the bonding surface. Alternatively, the adhesive may require application via costly specialized equipment like co-extrusion equipment.
Even more problematic to printing and packaging professionals is using ionic films to package items, such as food, medical devices or the like that require highly transparent and translucent packaging. Optical properties of polymer films, such as haze, transparency, clarity and transmittance are key issues in packaging applications, since they allow the consumer to see what is contained within the package. Hence the optical properties are important features in the marketability of a particular product.
Most conventional adhesives used on ionic films cause an undesirable chalky appearance in the packaged item since conventional adhesives are derived from polymeric components that have been coalesced prior to coating or polymeric materials having molecular weights of more than about 100,000 daltons which produces adhesive films with light transmission values of less than about 40%. In other cases, the adhesive may create blotches of chalkiness throughout the packaging to further reduce the attractiveness of the packaged item.
In an attempt to ameliorate the chalky appearance, printing and packaging professionals developed a method of coating an adhesive onto a bonding surface prior to adhesion to the ionic film using a vacuum-based process. Unfortunately, coating the bonding surface may partially or completely occlude any pores located in the bonding surface. Partial or complete occlusion of pores located in the bonding surface generally decreases a porosity of the bonding surface. Decreasing the porosity causes an increase in vacuum cycle time required for pulling the ionic film to the bonding surface during the vacuum-based adhesion process. Therefore, coating the adhesive onto the bonding surface prior to adhesion to the ionic film may increase the vacuum cycle time and thus, increase costs.